The Taoyuan International Airport Link (TIAL) is a metro system stretching from Taipei city center to Taoyuan International Airport with a total length of 51.0 km, which comprises 8 underground stations constructed by cut and cover method and 15 elevated stations. CECI Engineering Consultants, Inc. in Taiwan is in charge of detailed designs and primary construction supervision works on Packages DA115, DU01, DU02 and DE01. Some special issues about geotechnical design works in TIAL are introduced in this article.

1. Large-scale Excavation For A1 Station And Joint Development Buildings

A1 terminal station of TIAL is located asides the Taipei Main Station. The excavation was performed in very soft ground with high groundwater level and an aquifer underlying the excavation. A large-scale excavation with 27.2 m in depth and 26,000 square meters in area was constructed for A1 station as well as for the basement of joint development buildings having 76 stories and 56 stories, respectively. As indicated in Figure 1, the excavation site is situated next to many sensitive underground and above-ground structures, such as Taipei City Mall, viaduct, High Speed Rail (THSRC) and Taiwan Railway Administration tunnels etc., on which no adverse effects were allowed in order to ensure the normal operation. Protection measures, such as buttress and full height cross walls for diaphragm wall system and groundwater withdrawal from the underlying aquifer with intensive monitoring were employed to reduce deformation induced by the excavation and ensure the basal stability of excavation. Observations showed that lateral deformation up to 40 mm for diaphragm wall and surface settlement of 27 mm were found at the end of excavation.

Figure 1 Large-scale excavation for the terminal station of TIAL

2. DOT Tunnel Crossing Dan-Shui River

A tunnel works with a total length of 1580m will be performed to cross Dan-Shui River and connect Taipei main station and San Chong City. If twin bored tunnels are employed, up to six cross passages shall be installed according to Fire Protection Regulation. In order to eliminate risk in construction of cross passages as well as to save land compensation for the route running underneath residential houses located, a Double-O-Tube (DOT) shield machine was employed to replace twin bored tunnels through elaborative assessment (refer to Figure 2). Similar machine was successfully adopted in Japan and Shanghai, Mainland China before. The tunnel was mainly bored in silty clay and occasionally in sand, as shown in Figure 2. The maximum vertical slope and minimum horizontal curvature radius of the alignment is 4.9% and 277.0 m, respectively. DOT shield machine was launched from San Chong end in December 2009 and arrived at Taipei end in December 2010. >> Read More